PREDICTION OF ALLUVIAL CHANNEL PATTERN OF PERENNIAL RIVERS

Purely braided, meandering and straight channels can be considered as end-members of a continuum of alluvial channel patterns. Several researchers have succeeded in separating channel patterns in fields defined by flow related parameters. However, the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry. In this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains. The method is based on two, almost channel pattern independent, boundary conditions: median grain size of the river bed material, and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient. This can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition, P = 1. Based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with P > 1.5. The function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation, with a bankfull or mean annual flood discharge above 10 m(3)/s and a median bed material grain size between 0.1 and 100 mm.